1. Field of the Invention
The invention relates to immunological methods and materials and more especially to methods and materials for determining minute quantities of antigenic materials. The term "antigenic materials" as employed in this specification means substances having chemically-defined molecules with which an antibody can react, and includes antigens and haptens.
2. Description of the Prior Art
There are known immunological materials, usually called liposomes, which comprise a lipid bilayer structure and which can contain entrapped markers. Sensitized liposomes have been described by Kinsky and others in for example Biochemistry, Vol. II, No. 22, 1972, pp. 4085-4093.
These sensitized materials may be prepared in known manner from an aqueous mixture of a phospholipid e.g. lecithin and/or sphingomyelin, a sterol, e.g. chlosterol, a charged amphiphile e.g. dicetyl phosphate, together with a fourth component, known as a sensitizer, which serves to render the product sensitive to lysis by a specific antiserum in the presence of complement. The sensitizer molecule comprises an amphiphilic body portion having an apolar tail and a polar intermediate portion to which is joined an antigenic head.
In the preparation of the liposomes or other lipid bilayer structure, an aqueous solution containing the marker is introduced, and the aqueous marker solution becomes entrapped by the lipid layers within the structure of the product. The marker serves to indicate lysis, since the released marker can be detected, and the quantity of marker released can be determined.
One especially preferred form of marker is the spin label type of marker as described by McConnell et al in Proc. Nat. Acad. Sci. USA Vol. 71, No. 5, pp. 1691-1964, May 1974. These spin label markers permit the application of very convenient electron spin resonance (ESR) techniques for monitoring the lysis. Other detectable marker materials can however be employed e.g. glucose as proposed by Kinsky et al.
Before the present invention these reagents and techniques have been employed mainly for studying matters of scientific interest in connection with the structure of and the mechanism of lysis of lipid membranes.